Various patents disclose methods and apparatus for blow molding a hollow thermoplastic article. See for example U.S. Pat. Nos. 3,137,748 and 3,288,898.
Also, a method has been disclosed in U.S. Pat. No. 3,330,006 for molding a container headpiece and closure structure onto a preformed thermoplastic container body.
More complicated processes for forming, blow molding, and filling a container are disclosed in the U.S. Pat. Nos. 3,464,085; 3,523,401; 3,597,793; 3,664,793; 3,674,405; 3,919,374; Re. 27,155 and patents cited therein.
Of particular interest is the method for forming and filling container with a plug attachment molded in the bottom of the container as disclosed in the U.S. Pat. No. 3,919,374. The method may be effected with apparatus of the type disclosed in the U.S. Pat. No. Re. 27,155. Specifically, a parison in the form of a hollow tube is continuously extruded by an extruder in a tubular shape between two coacting first or main mold halves. At the bottom of the main mold halves, a plug attachment, such as a rubber stopper, is positioned by means of a vacuum holder in a secondary cavity formed in the bottom portion of the main mold halves. The parison has a length sufficient that a portion of the parison extends below and about the stopper.
When the parison is of the desired length, the main mold halves are closed around the lower portion of the length of the parison. The upper portion of the parison extends out of the mold halves through a top opening defined by the closed main mold halves. When the main mold halves are closed, the parison which surrounds the stopper is pinched closed by coaction of the walls of the main mold halves and the stopper becomes integrally molded as part of the container bottom.
The length of the the parison is then cut off below the extruder and above the main mold halves with the upper portion of the cut-off length of the parison tube held open by a set of vacuum holding or gripping jaws.
Next, the assembly of the closed main mold halves and parison is moved to a position under a blowing and filling nozzle assembly. The vacuum holding jaws move with the main mold halves and continue to hold open the upper portion of the parison above the main mold halves. The blowing and filling nozzle assembly has a mandrel that is moved downwardly into the opening of the tubular parison until it presses the parison against the neck of the main mold top opening and forms a seal. The container is then formed by blowing filtered gas through a nozzle of the assembly into the parison to expand the parison outwardly against the walls of the main mold cavity. Vacuum can also be employed for this purpose in lieu of or in addition to blowing with gas.
Next, the compressed air is vented from the formed container through the assembly and a metered amount of liquid product is forced into the bottle through a fill nozzle of the assembly. As the product contacts the plastic walls, the container solidifies. The main mold halves may be internally cooled in some applications to promote more rapid solidification.
When the container is filled with the desired amount of liquid, the blowing and filling nozzle assembly is retracted to its original position. At this point in the cycle, the length of parison between the top of the main mold halves and the holding jaws is still soft or semi-molten. A separate pair of coacting second or upper sealing mold halves are then moved together around the exposed length of parison to form the container upper portion immediately above the container main mold halves and below the holding jaws.
After the container is sealed at the top, the container main mold halves and the separate upper sealing mold halves open, along with the parison holding jaws. The finished container, completely formed, filled, and sealed, is then conveyed out of the machine by conventional techniques.
Although the above-discussed method of U.S. Pat. No. 3,919,374 for forming and filling a container with a stopper molded in the bottom of the container works satisfactorily in many applications, there are conditions inherent in this method that must be recognized and accommodated by careful design and operation of apparatus for effecting the method so as to avoid or minimize certain problems.
First, with stopper feeding and placement occuring below the main mold halves, the stoppers can become contaminated by liquid product that may drip from the fill nozzles during the automatic cycling of the apparatus.
Second, conveyor mechanisms are typically required to move the stoppers under the mold halves below the extruder. Such conveyor mechanisms, requiring lubrication, cannot be easily sterilized. Non-sterilized conveyor mechanisms in close proximity with the stoppers may be undesirable when filling the blow-molded containers with sterile product.
Third, the inclusion of a stopper in the bottom of the container precludes the formation of a conventional flat bottom on the container. Thus, conventionally shaped, flat bottomed containers that are self-supporting cannot be made with a bottom inserted stopper.
Fourth, when a stopper is initally positioned in the bottom region of the open main mold halves, it is difficult to ensure that the extruding length of hollow tubular parison flows vertically downwardly, without curl, and then properly around the stopper. If the extruding length of hollow tubular parison does not properly surround the stopper at the bottom of the open mold halves, the subsequently molded container may have an improperly formed bottom with one or more accidentally formed apertures through which the filling product can drain and splash onto the stopper insertion mechanisms. This may contaminate other stoppers.
Fifth, where the stopper is positioned and molded at the bottom of the container, the stopper insertion mechanisms typically occupy a significant amount of space below the mold assembly which precludes the use of standard mechanisms for take-out and deflashing of the molded container.
Until the present invention, the various disadvantages associated with bottom stopper insertion techniques described above had to be accommodated. The present invention now substantially eliminates these disadvantages by providing a method and apparatus for molding a container without effecting any secondary stopper insertion operations at or in the bottom of the container during the molding of the container.
Further, the present invention contemplates, in general terms, a method and apparatus for effecting one or more secondary operations at the container top opening after the container has been molded, but before it has been sealed or, in some cases, even before it has been filled with the desired product. It would be desirable to provide such a method and apparatus wherein such secondary operations are effected at the top of the container so that the base of the container can be made substantially flat and smooth so that the container is self-supporting on its base.
Further, it would be advantageous to provide an attached, but removable, plug or stopper in the top of a flat bottomed container to prevent spillage during subsequent handling. Such spillage, in addition to obviously reducing the liquid content in the container, could contaminate the molding or filling mechanisms and other associated apparatus.
It would also be desirable with such a flat bottomed container to provide an attached plug or stopper in the top of the container wherein the plug is wholly or partially encapsulated or sealed by a formed extension of the container thermoplastic wall and wherein the formed thermoplastic extension could be severed from the containers when desired to permit access to or removal of the plug or stopper.